Light Phenomena: Refraction, Dispersion and Scattering

Dispersion is the phenomenon where white light splits into its constituent colors (the spectrum) when passing through a prism or similar medium.

At sunrise and sunset, sunlight travels through a thicker layer of the atmosphere. Blue light is scattered away, leaving mostly red light to reach the observer.

A rainbow is formed by the refraction, dispersion, and internal reflection of sunlight within water droplets in the atmosphere.

At noon, the sun is overhead, and light travels through a shorter path in the atmosphere. Because there is less atmosphere to pass through, there is minimal scattering of colors, so the sun appears white.

Violet light has the shortest wavelength and the highest frequency among visible colors, causing it to experience the greatest refractive index in a prism. Consequently, it deviates the most from its original path.

The blue color of the sky is caused by Rayleigh scattering, where shorter wavelengths of sunlight are scattered more efficiently by atmospheric gases than longer wavelengths.

Rayleigh scattering occurs when sunlight interacts with the gas molecules in Earth's atmosphere, such as nitrogen and oxygen. Because blue light travels in smaller, shorter waves, it gets scattered in all directions much more than other colors, making the sky look blue.

Twinkling of stars and the apparent position of the sun are classic examples of atmospheric refraction. The red color of the sun at sunset is caused by the scattering of light, not refraction.

Atmospheric refraction causes the sun to appear above the horizon when it is actually slightly below it, both at sunrise and sunset, adding approximately 2 minutes to each event.

Stars are point sources of light, so their light is easily disrupted by atmospheric turbulence, causing twinkling. Planets appear as extended sources, so their light averages out and they do not twinkle.

Due to the bending of light by the atmosphere, the sun becomes visible to an observer on Earth about 2 minutes before it actually crosses the horizon.

Red light has the longest wavelength in the visible spectrum, which means it undergoes the least scattering by particles in the atmosphere, allowing it to travel longer distances.

In a dispersive medium like glass, the refractive index is higher for shorter wavelengths. Since red light has the longest wavelength, it experiences the lowest refractive index and thus travels the fastest.

In the visible spectrum, violet light has the shortest wavelength, while red light has the longest.